Update gem dependencies
- Add Jekyll plugins needed for the theme to .gemspec
- Remove Jekyll plugin gems from example site as they are installed with the theme
Replace base_path with `absolute_url` filter where possible
Don't prepend `author.avatar` paths with `/` when path contains `://`
Remove `pre` from version and bump to 4.0.1
Update version to 4.0.0.pre
Allow images to be placed in other folders
- Remove `images/` only restriction and encourage placement in `assets/images/` instead
Remove _config.yml from root
Add example site for testing
Update files and directories ignored by Git